The proposed research is focused on the development of two separate time domain magnetic resonance spectrometers: one at a frequency of 140 GHz (1H frequency of 212 MHz, magnetic field of 5T) and the second at a frequency of 250 GHz (1H frequency of 380 MHz, magnetic field of 9T). These spectrometers will be the world's first high power time domain spectrometers operating at frequencies above 100 GHz where modern magnetic resonance experimental research is conducted. The application will be in time domain dynamic nuclear polarization/nuclear magnetic resonance (DNP/NMR) and EPR research. Currently, the full implementation of time domain magnetic resonance techniques at high frequency is restricted by the paucity of high frequency microwave amplifiers. The advent of high frequency microwave amplifiers will permit the development of polarization transfer methods based on coherent processes the integrated solid effect, the dressed state solid effect, electron-nuclear Hartmann-Hahn cross polarization, etc. -- which are more favorable at high magnetic fields. Gyroamplifiers are essential for the implementation of these time domain experiments. Time domain EPR spectroscopy will also benefit greatly from this new instrumentation. The higher frequency can offer increased g-factor resolution for spectra consisting of overlapping powder patterns, the more precise measurements of the relative orientation of g-, hyperfine and dipolar tensors, and it will further simplify the acquisition and interpretation of pulsed ENDOR spectra. Accordingly, the first goal of this proposal is to integrate an existing 820W, 140 GHz gyroamplifier with an existing NMR and EPR spectrometer and to obtain first demonstrations of the spectrometer in high power DNP/NMR and EPR research. We will use a versatile low temperature spectrometer designed for the study of DNP/NMR at 212 MHz and EPR at 140 GHz. We have recently successfully operated this spectrometer using a low power (120 mW) source, but must develop and implement the components needed for its use with the high power gyroamplifier source. The second goal is to design and demonstrate improved resonators for DNP/NMR and EPR, such as photonic crystal resonators, and to develop the necessary ancillary THz components for the NMR application, such as switches, circulators, transmission lines, etc. for THz DNP/NMR and EPR experiments. Because of the scarcity and high cost of commercial instrumentation at high frequencies, it is crucial to develop these components to efficiently transmit and apply the available coherent radiation. The third specific aim is to complete the development of an existing 14 W, 250 GHz gyroamplifier and to apply that amplifier to pulsed DNP/NMR and EPR research. We first plan to finish the development of this amplifier at a power level of > 100 W using improved gyroamplifier designs in the first year of the proposal. Once the 250 GHz gyroamplifier is fully developed, we will apply it to pulsed DNP/NMR and EPR. The resultant system will then be the highest frequency high power DNP/NMR and EPR spectrometer in the world.